Because of its low-density, high strength and toughness, beryllium is used widely in the manufacture of structural elements in precision inertial guidance instruments. For bearings for supporting rotating elements in such applications, beryllium is often coated with a ceramic layer for the load handling surface.
In such applications, high micro-yield strength of the beryllium structural element is desired along with toughness, and machining ease.
The micro-yield strength of beryllium has previously been improved by dispersion strengthening which may be achieved by a distribution of beryllium oxide particles within the beryllium matrix. The oxide particles of this material, however, become dislodged from their sites in the metal during the polishing process or in use and produce undesirable scratches on the surface of the beryllium element. Also, theory predicts that the strength properties of the beryllium element, thus produced, could be improved.
In the case where a ceramic coating is used either alone or with beryllium for precision bearings or other load handling applications, not only are machining, toughness and strength factors of interest, but thermal conductivity and expansion, friction, magnetic properties, and porosity become important. Ceramics typically have far lower thermal conductivity than the pure metal counterpart which impedes the removal of heat from the source at the bearing interfaces. Because the ceramic has a different thermal expansion coefficient from the pure metal which often constitutes the instruments structural members, instrument accuracy is reduced. Ceramics including nickel or iron tend to be magnetic and thus contribute to noise in the electromagnetic circuitry of inertial instruments. Sputtering or plasma spraying is commonly used to produce ceramic deposits on beryllium for bearings, due to the difficulty in mechanically forming ceramic elements. Sprayed layers are porous which, in the case of air bearings, causes a loss of bearing air pressure and stiffness, and, further, sputtered surface bearings suffer from anomalies in composition and adhesion which promote friction and high wear.